Method and apparatus for manufacture of a diaper with elastic margins

ABSTRACT

The present invention is a method and apparatus for making a diaper having one or more elastic margins. The diaper uses for the entire moisture permeable backing sheet an elastomeric material of the type that is heat unstable and relatively inelastic in its unshrunk form and stable and relatively elastic in its heat shrunk form. Diapers made using one of these materials as a backing sheet can be conventionally assembled. After assembly, the marginal areas, which may be either or both of the transverse and longitudinal margins, may be heated to a sufficient temperature for shrinkage to occur in the backing sheet. This shrinkage will only occur when the backing sheet is unrestrained. The method provides for the maintenance of longitudinal tension in the central portion of an end-to-end assembly of diaper units while relaxing the edge tension on the units. This is accomplished in the present diaper making machine by passing the assembly over a series of rollers which are of cylindrical form in the central portion and are tapered at each end. The marginal portions overhang the tapered portion where they are free to shrink after heating. If an elastic waist construction is desired, the diapers are similarly heated in a transverse direction whereupon any transverse tension is relaxed to enable transverse shrinkage to occur. While the preferred diaper uses the heat shrinkable material as the entire backing film, it is within the scope of the invention to insert ribbons of this material along the appropriate marginal edges of the diapers and use conventional backing film materials.

This application is a division, of application Ser. No. 850,183, filed4/10/86.

BACKGROUND OF THE INVENTION

The present invention comprises a disposable diaper having elasticizedleg and/or waist encircling areas, and a method and apparatus formanufacture of the diapers. The elastic areas are provided by a heatshrinkable elastomeric material of the type that is heat unstable andrelatively inelastic in its unshrunk form and stable and relativelyelastic in its heat shrunk form.

Garments having localized elasticized areas for ensuring relativelytight fits around such body zones as wrists, waist or thighs have longbeen manufactured. Initially, and still to a certain extent, the elastichas been applied by sewing while held in a stretched condition. Whenrelaxed, the elastic causes a shirring or puckering of the elasticizedarea of the garment. Sewing elastic is a relatively slow and expensivemanufacturing operation. Many inventors have dedicated their energy tofinding simpler methods of attaching elastic. As one example, Gray, U.S.Pat. No. 1,544,312, used a partially cured rubber strip which wasmechanically crimped to the garment and later heat cured. Maxey, U.S.Pat. No. 2,905,181, used a band of nitrile rubber which was heat sealedto a moisture impervious polyvinyl chloride film.

Disposable diapers for infants have been the subject of a great deal ofinventive activity to prevent leakage. One very successful effort inthis regard was the use of a box pleat around the thigh areas of aninfant. A diaper of this type is described by Duncan et al in U.S. Pat.Reissue No. 26,152. While this construction represented a major stepforward, it still did not provide an entirely satisfactory solution tothe problem of leakage. Another move toward an ultimate solution isdescribed by Buell in U.S. Pat. No. 3,860,003. The Buell diaper usednarrow ribbons of stretched elastic along each longitudinal side marginin the thigh encircling areas. This construction has been so highlysuccessful that it has been emulated and improved upon by subsequentinventors in the field. The following U.S. Pat. Nos. are exemplary ofthese later developments: Woon et al, 4,050,462; Strickland et al,4,253,461; Sigl et al, 4,437,860; and Teed, 4,405,397. The Strickland etal product represents a move beyond diapers suitable only for infantsand is a product principally adapted for use by incontinent adults.Schaar, in U.S. Pat. No. 3,951,150, shows an infant diaper having anelasticized waist encircling area designed for reducing leakage fromthat portion of the product.

The above list is presented primarily to indicate historical developmentof diapers having elasticized zones and is not intended to be fullyinclusive of all such products which have been developed. All of theseexamples use an elastic material which is normally a relatively narrowribbon of natural rubber adhesively bonded between the backsheet andcover sheet of the diaper. The use of adhesive bonding, usually withflexible hot melt adhesives, has enabled the production of elasticizeddisposable diapers at high rates of speed.

During the later part of the time period represented by the abovepatents, a parallel approach has been developing using non-rubberelastomeric materials. These are based on a wide variety of syntheticpolymers which typically are uniaxially or biaxially stretched duringtheir manufacture into relatively thin film. This stretching inducesstresses which are frozen into the product when it is cooled while beingheld under uniaxially or biaxially applied tension. Certain of thesematerials retain a memory of their dimensions in the originalunstretched state. Depending on the particular polymer chosen, and itsmethod of manufacture, by heating to a specific predeterminedtemperature, the material will shrink back to approximately thisoriginal dimension. These polymeric products can be readily tailored tobe of elastomeric nature. The term "elastomeric" is interpreted invarious ways, but here it is generally meant to mean that a product maybe stretched to at least about 120-140% of its original length andreturn to that length without permanent deformation when the stretchingforce is released. Many of the products available are relativelyinelastic in their uni- or biaxially oriented heat unstable forms andwould not meet the above criterion. However, these become fully elasticwhen heat shrunk. A further feature of many of these polymers is thatthey can be heat sealed or bonded to other materials at a temperaturebelow the point which will cause heat shrinkage. This is especiallyconvenient for the manufacture of elasticized garments since it infersthat the material may be applied without the need to be held undertension. A subsequent heating step is all that is needed to produce anelasticized zone.

While many polymeric materials of generically different types can becited as being useful in the above application, the following U.S. Pat.Nos. should be considered as being exemplary: Perrin et al, 2,200,249;White, 2,953,551; Cook et al, 3,086,242; Holden et al, 3,265,765; andPellicciari et al, 3,551,540. The following British patents Nos. alsodisclose useful polymer compositions: 866,819; 866,820; 866,821;866,822; and 1,010,064.

The original application of heat shrunk elastic to garments appears tohave been done by Mason as shown in U.S. Pat. No. 3,245,407. Here theinventor produced plastic panties with heat shrunk elasticized leg andwaist zones. Mason showed other applications as well. Later, Althouse inU.S. Pat. No. 3,639,917 showed the use of heat shrinkable elasticribbons in other applications such as wrist cuffs on disposable hospitalgarments. Massengale et al, in U.S. Pat. No. 3,819,401, and Koch et al,in U.S. Pat. No. 3,912,565 show the use of specific heat shrinkablematerials for making elasticized areas in garments such as panties.Schirmer, in U.S. Pat. No. 3,755,062, shows the use of a film of heatshrinkable materials for making bulked fabric articles such as nonwovenrugs.

Natural rubber is a relatively expensive product and for this and otherreasons, it is normally used in the form of threads or relatively narrowribbons when used to elasticize portions of garments. A disadvantage ofthis construction is that the elasticized portion of the garmentfrequently presents a small and very narrow bearing area against theskin of the wearer. Thus, if the purpose of the elasticized area is toprevent leakage, as in the case of an elastic leg diaper, the elasticmust be held under relative high tension to provide a tight seal. Thiswill frequently result in chafing and general discomfort to the wearer.One solution to this problem has been to use parallel narrow strips ofrubber elastic to increase the bearing area. A diaper having this typeof construction is seen in Repke, U.S. Pat. No. 4,430,086. While thisapproach has been effective, it is relatively expensive because of theadditional elastic required. It also considerably complicatesmanufacture of the product. For this reason, disposable diaper designershave turned to the use of heat shrunk elastomers which can be used inthe form of relatively wider ribbons to increase bearing area.

Heat shrinkable materials became of interest to diaper designers asanother method for overcoming the cutting and chafing problem caused bynarrow elastic. A considerable number of patents have issued, beginningabout 1980, directed to the use of heat shrinkable elastic ribbonsplaced in marginal areas of disposable diapers. In some of these theheat shrinkable elastomer is used only in the leg area, along thelongitudinal margins. In others it is used only in the waist area alongthe transverse margins of the diaper. In still other constructions, theheat shrinkable elastic is used in both locations. Representativeexamples of disposable diapers using heat shrunk elastic are found amongthe following U.S. Pat. Nos.: Repke et al, 4,205,679 and 4,430,086;Mesek et al, 4,324,245 and 4,352,355; Pieniak, 4,333,782; Pieniak et al,4,337,771 and 4,413,623; Sciaraffa et al, 4,381,781; Sigl, 4,486,192;Kievit et al, 4,515,595; and Relter, 4,563,185. The following Britishpatent applications Nos. are also of interest: Lash, GB 2,136,677A andChapman et al, GB 2,136,678A.

All of the above patents use discrete ribbons of the heat shrinkableelastic material. These differ greatly in configuration, location,method of attachment, and area in which they are heat shrunk.

The inventors of the above diapers have not discussed suitable equipmentfor manufacturing them at any length. In making an elastic leg diaperhaving rubber elastic, an end-to-end assembly is normally held undersufficient tension during manufacturing to prevent wrinkling of theedges. U.S. Pat. Nos. to Buell, 4,081,301; Gore, 4,239,578; Teed,4,309,236, 4,325,372, and 4,405,397; Frick 4,397,704; and Frick et al,4,371,417 are exemplary of patents showing equipment for the insertionof elastic along the longitudinal edges of disposable diapers. Sigl,U.S. Pat. No. 4,412,881 and Sabee, U.S. Pat. No. 4,227,952 showequipment for insertion of discrete lengths of tensioned elastic alonglongitudinal edges. In addition, these following U.S. Pat. Nos. showmethods and apparatus for inserting elastic inserts transversely acrossthe ends of diapers forming the waist portions: Kiela, 3,844,288; Rega,4,240,866; Joa, 4,284,454; and Pieniak, 4,488,923. Klasek, in U.S. Pat.No. 4,293,367 shows a method and apparatus for contouring elastic aroundlongitudinal leg cutouts of disposable diapers. This list is cited asbeing exemplary only and is not intended to be all inclusive. None ofthe patents noted above are specifically concerned with the insertion ofan untensioned heat shrinkable polymer ribbon and its subsequent heattreatment.

SUMMARY OF THE INVENTION

The present invention concerns a method and apparatus for themanufacture of diapers having elastic leg and/or waist areas formedusing areas of heat shrinkable elastomeric materials located in theappropriate marginal zones of the diaper. These heat shrinkableelastomeric materials are those which are heat unstable and relativelyinelastic in their unshrunk form and stable and relatively elastic intheir heat shrunk for. They may comprise discrete strips located alongthe appropriate marginal areas of the diapers. Alternatively andpreferably, the entire moisture impermeable backing sheet of the diapercomprises the heat shrinkable elastomeric material.

The invention is also considered to include disposable diapers havingmarginal elastic leg and/or waist areas made using the heat shrinkableelastomeric material as the entire moisture impermeable backing sheet ofthe diaper unit.

The method includes uniting the individual diaper components to form acontinuous end-to-end or side-by-side assembly of diaper units, theend-to-end relationship being preferred. The area adjacent adjoiningdiaper units preferably forms the waist encircling areas of the diapers.These assemblies are maintained under sufficient longitudinal tension toprevent wrinkling during the manufacturing process. At some point anappropriate area of the longitudinal edges of each diaper unit is heatedto a temperature sufficiently high to enable shrinkage of theelastomeric material. Immediately thereafter the marginal longitudinaltension is relaxed while tension is maintained in the central portion ofthe assembly. The marginal tension is kept in relaxed condition for asufficient time for the heated elastomeric material to shrink and coolto a temperature where it is again stable, thereby creating marginalelasticized zones on the diapers.

A major element of novelty of the present invention is the provision formaintaining tension along the central portion of the assembly of diaperunits while relaxing the tension along the margins to permit essentiallyfree shrinkage of the heated portions. This is accomplished by runningthe assembly after marginal heating over a series of rolls which arecylindrical in the central portion but tapered at each end. The heatededges of the diaper overhang the tapered portions. In this manner, asthe edges shrink the circumferential distance they travel over thetapered ends of the rolls is significantly less than the circumferentialdistance traveled by the central portion of the diaper assembly. Asufficient number of rolls are employed to permit the desired marginalshrinkage to occur and to further allow the heated areas to cool to thepoint that they are again stable. At some point beyond this, when theheat treated and now elastic marginal portions have again become stable,they can once more be stretched, if desired, as the assembly movesfurther through the diaper making machinery. The diapers may also oralternatively be heated transversely to produce elasticized areas. Thisis preferably done by heating the appropriate localized areas with a hotroll or other means. Preferably, simultaneously with the heating orimmediately thereafter, individual diapers are severed from the diaperunits to release any transverse tension that might be present. Thispermits the heat treated end portions of the diaper units to shrinkfreely until they have sufficiently cooled to become heat stable andelastic. Alternatively, the diaper assembly is allowed to remain intactduring transverse shrinkage and the transverse tension is relaxed bysome other means, such as festooning the assembly between two rollpairs.

The equipment and method just described can be used with marginalribbons of the heat shrinkable elastic material which are inserted intoappropriate locations during diaper assembly. However, in order tosimplify construction, it is preferable to make the entire backing sheetof the heat shrinkable polymeric material. Only those marginal zoneswhich are to be elasticized are heated and allowed to shrink aspreviously described.

It is an object of the present invention to provide a method andapparatus for the manufacture of disposable diapers or similar productshaving marginal elasticized areas.

It is also an object to provide a method and apparatus for makingdisposable diapers having elasticized marginal areas using a heatshrinkable polymeric material which is elastic after being heat shrunk.

It is a further object to provide a method and apparatus in which thelongitudinal marginal areas are heat shrunk by relaxing the tensionthereon while maintaining tension on the central portion of anend-to-end assembly of diaper units.

It is still a further object to provide diaper manufacturing machineryhaving double end tapered rolls to permit heat shrinking of marginallyheated areas.

It is yet another object to provide a new disposable diaper or similarproduct having marginal elasticized zones in which the entire backingsheet is made of a heat shrinkable polymeric material.

These and many other objects will become readily apparent to thoseskilled in the art upon reading the following detailed description takenin conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 3 and 5 show various embodiments in plan view of disposablediapers of the present invention prior to heat shrinkage of the elasticareas.

FIGS. 2, 4, 6 and 7 show similar embodiments after the elastic areashave been heat shrunk.

FIG. 8 shows a representation in right side elevation of manufacturingequipment for the disposable diapers of the present invention.

FIGS. 9 and 10 are more detailed top plan and right side views,respectively, of the longitudinal edge heat shrinking station of theequipment.

FIGS. 11 and 12 are right side views of two embodiments of a transverseedge heat shrinking station of the equipment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description that follows, it will be understood by those skilledin the art that certain terms are relative. Most disposable diapers andadult incontinent pads are assembled in a continuous end-to-end fashion.In this case the sides of the diaper, which wrap around the upper thighsof the wearer, are the longitudinal direction. However, it is known fordiapers to be manufactured in a continuous side-to-side assembly as, forexample, is shown in Joa, U.S. Pat. No. 4,284,454. In this case, theends, or waist encircling portion of the diaper is in the longitudinaldirection of motion during manufacture. Thus, the terms "longitudinal"and "transverse" are relative and as used herein should not beconsidered as limiting to one orientation or the other.

The various embodiments of the present invention can most readily beunderstood by reference to the figures. FIG. 1 shows a diaper 2' whosecomponents have been fully assembled but which is as yet in anunfinished state of manufacture. This is the form of a diaper unit asthey are most commonly found while under light tension in an end-to-endassembly on a diaper making machine. It comprises a moisture imperviousbacksheet 4 which, in the present case, is a biaxially oriented heatshrinkable thermoplastic material. This backing film is shown here inits relative inelastic heat unstable, unshrunk state. When heat shrunk,it becomes elastic having an extensibility of up to 100%, or evengreater. Backing sheet 4 is overlaid by a moisture absorbent flufffiller pad 8. This, in turn, is covered with a moisture perviousnonwoven top sheet 6. The entire assembly is bonded together by aplurality of fine hot melt adhesive lines 9. Each diaper unit haslongitudinal margins 10 which define the leg encircling crotch areas andlongitudinal margins 12 which are located in waistband area. The diapersfurther have transverse margins 14 which further define the ends of thewaistband areas. Adhesive attachment tapes 16 complete the unit.

FIG. 2 shows the diaper of FIG. 1 in which the longitudinal margins 10have been heat shrunk in the leg encircling areas to form elasticportions. These ensure a tight fit and are important in preventingleakage when worn by an infant or adult user. The diaper of FIG. 2 isshown without any longitudinal or transverse restraint. As a result, theheat shrunk marginal areas 18 will tend to form a shirred or wrinklededge 20 with accompanying transverse folds. When placed on a wearer theshirred edge 20 is generally placed under tension and the diaper surfaceis again drawn reasonably flat.

The temperature to which the longitudinal edge of a diaper of the typeshown in FIGS. 1 and 2 must be heated is dependent upon the particularpolymeric material which is used. These temperatures will generallyrange between about 80°-120° C. The amount of shrinkage obtained issomewhat dependent upon the temperature to which the polymeric materialis heated and the manner in which it is allowed to relax while beingcooled. These points will be discussed later in considerable detail.

An alternative manner of making a similar elastic leg diaper to thatshown in FIGS. 1 and 2 is seen in FIGS. 3 and 4. It might be noted herethat in all of the figures, like numbers indicate like components. Thediapers shown in FIGS. 3 and 4 are of a more conventional constructionsimilar to that in which rubber elastic is used in the leg encirclingareas. Here the backing film is of a more conventional material 5 whichwould typically be pigmented polyethylene film having a thickness in therange of 0.02-0.04 mm. In the present case, longitudinal ribbons 22 ofthe heat shrinkable polymeric material are placed along eachlongitudinal edge of the diaper. These would generally be of a width inthe range of about 10-15 mm and may run the full length of the diaper,as shown in FIG. 3. Alternatively, they may be discrete lengths ofmaterial located only in the crotch encircling area parallel tolongitudinal edge 10. FIG. 4 shows the diaper assembly of the diaperunit of FIG. 3 after the polymeric tape has been heat shrunk along themarginal area 10. This results in a longitudinal and transverseshrinkage to the range of 50-80% of original dimensions in the heatedarea to produce an elastic area 24. The end portions of tape 22 locatedin the waist areas of the diaper remain in the original unshrunk form.

FIGS. 5 and 6 show yet another version of a diaper employing heatshrinkable polymeric material to create elasticized areas along both theleg and waist encircling portions of the diaper. Again, as shown inFIGS. 3 and 4, the backing sheet is a conventional material such aspigmented polyethylene. In the present construction discrete lengths ofheat shrinkable polymeric material 26 are placed in each leg encirclingarea of the diaper. Similarly, transverse heat shrinkable ribbons 28 arelaid across each waist area of the diaper. Machinery to lay up a diaperof the type shown in FIG. 5 is conventional to this point. As oneexample, the longitudinal polymeric ribbons 26 may be placed in theassembly by any of the assembly machines previously noted that aredesigned to lay in discrete lengths of elastic. However, here theribbons 26 are not stretched when put in place. The transverse ribbons28 could conveniently be placed by machinery such as that described byFrick in U.S. Pat. No. 3,758,363. FIG. 6 shows the diaper unit of FIG. 5after the polymeric ribbons have been shrunk to produce longitudinalelastic zones 30 and transverse elastic zones 32. As shown in theprevious examples, this results in a shirred longitudinal edge 20 and,additionally, a shirred transverse edge 34. This construction helps toensure a tight, leak-proof fit in both the leg and waist areas.

FIG. 7 shows a diaper of similar construction to that shown in FIGS. 1and 2 in which the entire backing film is the heat shrinkablethermoplastic polymeric material. Here again, both the leg and waistencircling areas have been heat shrunk to produce elastic zones 18 and36, respectively. The present method has an additional importantadvantage shown in FIG. 7. It is a very simple matter to elasticize theentire leg cutout area so that the transition zones 21 are also elastic.This ensures a tighter fit around the entire thigh area of the wearer.

There are major advantages to the manufacturer in producing diapershaving the configuration of those shown in FIGS. 1, 2, and 7.Manufacturing equipment is much simpler since no provision need be madefor inserting either longitudinal or transverse elastic. The backingfilm itself serves this purpose. However, one further complication ispresent which had not been adequately solved until the present time,especially in the case of heat shrinking in the longitudinal or machinedirection. As noted earlier, after the heat shrinkable material has beenheated to a sufficient temperature at which shrinkage can occur, anyrestraining tension which would tend to prevent such shrinkage must beremoved. Diapers are normally manufactured under some longitudinaltension in order to prevent wrinkling during manufacture. This tensionis also necessary to ensure that the timing built into various machinecomponents does not fall out of synchronization resulting inmisassembled diaper components. The application of longitudinal tensionalso unavoidably causes a lesser amount of transverse tension on thediaper assembly. Thus, in order to effectively use the heat shrinkableelastomeric materials, conflicting demands must be met. Somehow tensionmust be maintained on the end-to-end diaper assembly to meet the machinedemands, yet the tension must be relaxed at least for a sufficient timeto enable shrinkage to occur in any heated areas. The present design ofa diaper manufacturing machine has successfully accommodated theseconflicting requirements as they apply to both longitudinal andtransverse heat shrinkage.

Machinery suitable for manufacture of diapers similar to those justdiscussed is shown in FIGS. 8 through 12, with FIG. 8 being an overallview. Here the moisture impervious backing sheet 4 is withdrawn from asupply roll 7 by feed rolls 40, 41. The fine line pattern of hot meltadhesive 9 may be applied to the backing sheet by an applicator 38. Ifthe backing film is not a heat shrinkable material in its own right,marginally located longitudinal ribbons 22 of such a material may beapplied to the backing sheet between rolls 40 and 41. A flexibleadhesive applied by applicator 39 may alternatively be used to create agreater bonding area between marginal ribbons 22 and backing sheet 4than would otherwise be provided by the adhesive fine lines 9. Asanother alternative, the heat shrinkable film 22 could be bonded by heatsealing, using a temperature below that at which significant shrinkageoccurs. Other bonding techniques such as ultrasonic welding may be alsobe employed when separate ribbons of the heat shrinkable material areused in the diaper construction. The heat shrinkable ribbon 22 may alsobe applied to the cover sheet 6 if desired.

The backing material 4, which may now have marginal ribbons 22 attached,enters a diaper component assembly conveyor 44 between pressure rolls 46and 48. At this point the moisture pervious top sheet 6 and the moistureabsorbent pads 8 are combined with the backing sheet. Pads 8 have beenpreformed and severed into units as they advance on conveyor 42. Theend-to-end assembly of diaper units 2 moves along conveyor 44 until itencounters opposing rolls 50 and 54. Roll 50 has a pair of heated shoes52 mounted so as to engage each longitudinal edge of the diaper units inthe leg encircling areas. These hot shoes will heat the heat shrinkablethermoplastic film to a temperature which will normally be at least 80°C.

As an alternative to the construction shown, roll 50 with hot shoe 52and backup roll 54 could be reversed so that the heat is applieddirectly to the backing film.

Immediately after leaving the heating area on conveyor 44, the diaperassembly passes over a plurality of rolls where longitudinal marginshrinkage occurs. Normally at least three such rolls 56, 58, 60 areemployed and more may be used if additional time is required forshrinkage and cooling until a heat stable state is again attained. Rolls56, 58, and 60 are generally cylindrical in their central section buttapered at each end. This construction is best seen in FIG. 9. Whilepassing over the rolls, normal tension is maintained in the central orpad area of the diaper assembly. However, the now heated longitudinalmarginal areas, which overhang over the tapered portion of the rolls,are free to shrink to the point at which the tapered portion of the rollis encountered. If shrinkage to 50% of the original longitudinaldimension is desired in the leg encircling areas, the circumference ofthe tapered portion at which the marginal area will ultimately berestrained should be half that of the circumference of the centralportion of the rolls. The use of these double tapered rolls is at theheart of the present method and apparatus. It is these rolls that enablethe conflicting demands for maintenance of longitudinal tension andrelaxation of marginal tension to be met.

After the marginal areas of the end-to-end diaper assembly have beenshrunk and are again heat stable, they pass from the double taperedrolls onto an additional conveyor 62 between rolls 64, 66 which serve tomaintain tension on the units. Rolls 68, 70 at the discharge end ofconveyor 62 serve a similar purpose.

If the diaper waist areas are also to be elasticized, they may at thispoint pass between rolls 72, 78. Roll 72 has a hot shoe 74 which istimed to engage and heat the end or transverse margins of the diaperunits. This roll may also have a severing knife 76, in which case roll78 serves as an anvil roll. Alternatively, the severing knife may be ona separate roll 77 located immediately after the roll pair 70, 72 (FIG.12). The now severed individual diapers 3 pass onto another conveyor 80between rolls 82, 84. Conveyor 80 moves at a somewhat faster speed thanconveyor 62 so that the diapers are separated by a small interval. Allrestraining forces on diapers 3 are released while they are traveling onconveyor 80. At this point the end margins are free to contract and coolto their stable elastic condition. The diapers move from conveyor 80 toconventional machinery, not shown, where they are folded and packaged.

The preferred form of the present invention utilizes the heat shrinkablethermoplastic film as the entire backing film for the diaper and doesnot utilize longitudinal or transverse heat shrinkable inserts such asare employed in the embodiments shown in FIGS. 5 and 6. However, whereit is desired to use transverse inserts 28, these may be applied at anyconvenient location prior to assembly of the individual components onconveyor 44. As noted earlier, apparatus for performing this step isconventional. Conveniently the transverse inserts might be applied tobacking film 40 at some point between feed rolls 40, 41 and assemblyrolls 46, 48 on conveyor 44. Many other such variations will be apparentto those who are skilled in the art.

EXAMPLE

The various components used in the manufacture of infant diapers oradult incontinent pads are well known within the industry. The moisturepermeable top or body contacting sheet has a basis weight usually in therange of 18-26 g/m² and may typically be a carded polyester fiber with alatex binder or spun bonded polypropylene having continuous fibers of2-5 denier thermally bonded by patterned calendar rolls. Respectiveexamples of these types would be Scott 6822, available from Scott PaperCompany, Nonwovens Division, Philadelphia, Pa. or Celestra, availablefrom Crown Zellerbach Corporation, Washougal, Wash. The moistureimpermeable diaper backing sheet may be a low density polyethylene filmhaving a thickness in the range of 0.02-0.04 mm (0.75-1.5 mils). Thismaterial is frequently microembossed to better retain attachment tapes.An example of such a conventional backing material would be Clopay Code53, available from Clopay Corporation, Cincinnati, Ohio.

The preferred backing film is a biaxially oriented heat shrinkableelastomeric material of the type that is heat unstable and relativelyinelastic in its unshrunk form and stable and relatively elastic in itsheat shrunk form. This may be used either for the entire backing sheetor for ribbon-like inserts along the marginal portions of the backingsheet. One such material is Cryovac SDX-0820, available for CyrovacDivision, W. R. Grace Company, Duncan, S.C. This material is a biaxiallyoriented irradiated polyethylene that becomes heat shrinkable attemperatures generally falling within the range between 80°-95° C.Unrestrained shrinkage after heating this material to the abovetemperature range will generally be to about 50% of original dimensions.Lower shrinkage can be achieved in one of several ways. Control of theamount of stretch during film formation is one suitable way. As oneexample, if it is only desired to produce elasticized leg opening areason a diaper, a uniaxially oriented film would normally be quitesuitable. Control of temperature to which the film is heated, and thesubsequent rate of cooling, is another way in which shrinkage can becontrolled.

Flexible rapid setting hot melt adhesives, which may be used to bindseparate heat shrinkable ribbons and may also be used as the fine lineadhesives for uniting the entire assembly, are commonly formulated fromethylene-vinyl acetate resins used with tackifiers and other additives.These adhesives tend to be somewhat tacky and flexible at roomtemperature. One suitable material is available from H. B. FullerCompany, Vadnais Heights, Minn. as Type HL 1048N.

Large sized infant diapers were made using the above Cryovac material inplace of the more conventional polyethylene as the moisture imperviousbacking film. These diapers were 495 mm long and 337 mm wide and weigheda total of 72 g. The pad was fluffed bleached kraft softwood pulp havinga density in the range of 0.07-0.08 g/cm³. The backing film had athickness of 0.015 mm. It is possible to use a film this thin becauseits tensile strength is approximately twice that of the normal lowdensity polyethylene film used for the backing material. The diaperswere conventionally assembled. After this the longitudinal margins wereheated to a temperture of approximately 95° C. over a width of about 10mm and allowed to shrink. Subsequently, the transverse waist areas ofthe diapers were heated to a slightly lower temperature over a width ofabout 15 mm and allowed to shrink freely. The ultimate diaper had anextensibility in the leg area of approximately 100% with about 40%extensibility in the waist areas.

It will be readily apparent to those skilled in the art that manyvariations could be made without departing from the spirit of thepresent invention. Thus, the invention is to be considered as beinglimited only by the following claims.

We claim:
 1. A method of making a disposable diaper of the type having amoisture permeable skin contacting cover sheet, a moisture impermeablebacking sheet, and a moisture absorbing filler pad disposed therebetweenwhich comprises:uniting the individual diaper components to form acontinuous end-to-end or side-by-side assembly of diaper units;providing areas of heat shrinkable elastomeric material at least alongone longitudinal edge of the diaper assembly, said elastomeric materialbeing of the type that is heat unstable and relatively inelastic in itsunshrunk form and stable and relatively elastic in its heat shrunk form;maintaining sufficient longitudinal tension on the diaper unit assemblyto prevent wrinkling thereof; heating the longitudinal edges of eachdiaper unit in the assembly in the areas of the heat shrinkableelastomeric material to a temperature sufficient to enable shrinkage ofsaid elastomeric material; immediately thereafter relaxing thelongitudinal edge tension of the heated diaper units while maintainingsaid tension in the central portion of the diaper units for a timesufficient to permit the heated elastomeric material to shrink and coolto a temperature where said elastomeric material is stable, therebycreating marginal elasticized zones on said diapers.
 2. The method ofclaim 1 wherein said relaxing includes passing the assembly of diaperunits over a series of transversely oriented rolls immediately followingsaid edge heating, the rolls being essentially cylindrical in theircentral portion but tapered at each end so that the longitudinal edgesof the diaper assembly overhang the tapered ends, whereby the distancetraveled by said longitudinal edges of the diaper unit assembly aresufficiently less than the distance traveled by the central portion ofdiaper units so as to relax the longitudinal marginal tension.
 3. Themethod of claim 2 which includes providing at least three end taperedrolls.
 4. The method of claim 1 wherein said providing step includes aseparate strip of heat shrinkable elastomeric material is placed alongeach longitudinal edge of the diaper units.
 5. The method of claim 1 inwhich the entire diaper backing sheet comprises heat shrinkableelastomeric material.
 6. The method of claim 1 in which the diaper unitsin the assembly are in an end-to-end relationship so that thelongitudinal edges of the diaper units correspond to the leg encirclingportions and the area adjacent adjoining diaper units forms waistencircling portions of the diapers.
 7. The method of claim 6 in whichsaid waist encircling areas of the diapers are essentially devoid offiller pad and which further includes providing areas of heat shrinkableelastomeric material in at least one of said waist encircling areas ofeach diaper unit, heating said heat shrinkable material in the waistareas following shrinkage of the elastomeric material in thelongitudinal edge zones, and relaxing any transverse tension present topermit the heated elastomeric material to shrink and cool to atemperature where said elastomeric material is stable thereby creatingelasticized waist areas in the diapers.
 8. The method of claim 7 whereinsaid transverse relaxing includes simultaneously with said heating orimmediately thereafter severing the individual diaper units from thecontinuous assembly.
 9. The method of claim 8 wherein a separate stripof heat shrinkable elastomeric material is placed in said waist areas.10. The method of claim 8 wherein the entire diaper backing sheetcomprises heat shrinkable elastomeric material.
 11. In a machine formanufacturing disposable diapers by combining a moisture permeable skincontacting cover sheet, a moisture impermeable backing sheet, and amoisture absorbing filler pad disposed therebetween, said diapersfurther having areas of a heat shrinkable elastomeric material in atleast one edge thereof, the improvement which comprises:means forassembling and combining the cover sheet, backing sheet, filler pad, andheat shrinkable elastomeric material into a continuous end-to-end orside-by-side assembly of diaper units; means for maintaininglongitudinal tension on the diaper unit assembly; means for heating thelongitudinal edges of each diaper unit in the areas of the heatshrinkable elastomeric material to a temperature sufficient to enableshrinkage of said elastomeric material; roll means positionedimmediately following said heating means for relaxing the longitudinaledge tension on the diaper unit assembly while maintaining said tensionin the central portion of the diaper units, said roll means comprising aseries of transverse rolls that are essentially cylindrical in thecentral portion but tapered at each end, so that the diaper edgesoverhang the tapered portions and the distance traveled by the marginalportions of the assembly when passing over the roll means is less thanthe distance traveled by the central portion of the diaper units,whereby the heated areas are enabled to shrink unrestrained and cool toa stable heat shrunk state in order to create marginal elasticized zoneson the diapers.
 12. The apparatus of claim 11 in which the roll meansincludes at least three end tapered rolls.
 13. The apparatus of claim 11in which the diaper component assembling means forms an end-to-endassembly of diaper units so that the area adjacent adjoining diaperunits contains the waist encircling portions of the diapers.
 14. Theapparatus of claim 13 which further includes transverse heating meansfor heating the heat shrinkable elastomeric material in at least one ofsaid waist encircling areas of each diaper unit to a temperaturesufficient to enable shrinkage of said elastomeric material, saidtransverse heating means being located sufficiently downstream so as tosequentially follow the heating, shrinkage and cooling of theelastomeric material along the longitudinal edges, and means followingsaid heating means to relax any transverse tension on the diaperassembly so that the heated transverse elastomeric material is allowedto shrink and cool while unrestrained.
 15. The apparatus of claim 14wherein said transverse relaxing means includes transverse severingmeans located adjacent to said transverse heating means to sever theindividual diaper units from the continuous assembly simultaneously withor immediately thereafter exposure to said transverse heating means. 16.The apparatus of claim 15 which includes transverse heating means toheat both waist encircling areas of each diaper unit.